Bacteria of the genus Chlamydia are significant pathogens of animals and man. The diseases caused by Chlamydia spp. in man include pneumonia, endocarditis, polyarthritis, blindness, and a wide range of sexually transmitted diseases including cervicitis, salpingitis, pelvic inflammatory disease, and infertility in females;and non-gonococcal urethritis and acute epididymitis in males. Chlamydia has also been implicated as a cofactor in a variety of chronic diseases such as coronary heart disease. Despite many years of effort, the Chlamydia remain intractable to genetic analysis due to their obligate intracellular lifestyle and complex developmental cycle. No one has been able to introduce foreign DNA into this organism and achieve stable inheritance of and expression of the foreign genes. Our long-term goal is to apply the power of genetics to study the pathogenic mechanisms of Chlamydia. The aims of this proposal include the development of genetic tools for the analysis of Chlamydia pathogenesis and hypothesis-driven aims to address specific questions of Chlamydia biology. The specific aims are to: 1) develop a method for introduction, expression, and stable maintenance of foreign DNA in Chlamydia and a system for gene replacement in Chlamydia;2) characterize the pathway for peptidoglycan synthesis mChlamydia;and, 3) identify the transport system for uptake of essential constituents for Chlamydia growth, specifically the source of methyl donors for methyltransferases. We will employ genetic, biochemical and cell biology strategies to each aim. Success in achieving the first aim will have a significant impact on Chlamydia research by making new tools for genetic analysis of Chlamydia available. Rapid advances in our understanding of Chlamydia pathogenesis and biology as well as the ability to construct Chlamydia mutants for vaccine development will be made possible by these new techniques. Success in aim 2 will finally resolve the chlamydia anomaly while aim 3 will attempt to resolve another apparent paradox of Chlamydia biology. Thus, these two aims will resolve some long-standing questions of Chlamydia biology and extend our knowledge of the intracellular lifestyle of this important pathogen..